Dictyostelium discoideum is a cellular slime mold existing as independent-living amoebae until an aggregation of the cells results in the formation of multicellular pseudoplasmodia. Cell contacts and interactions are necessary for the subsequent differentiation of the mature stalk and spore cells composing a fruiting body. The interactions between cells appear to depend upon the plasma membranes which undergo major changes in ultrastructure and antigen composition. The proposed research concerns the changes which may occur in the plasma membrane lipids and glycoproteins during the transition from the vegetative stage to the multicellular stages of the wild-type strain. Aggregateless mutants which do not differentiate will be utilized in the research. This study will involve the incorporation and the distribution of appropriate tritiated lipids and sugars in the plasma membranes at different stages and in different cell types. The incorporation of the labeled materials will be detected by autoradiography and scintillation spectroscopy. The information obtained by the uptake studies may provide clues to the nature of the plasma membrane changes which initiate cell interactions resulting in differentiation.